Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$9.98	9.397%	$10.9178	$10.92	$10.90	$10.90
Purchase #2	$247.93	3.436%	$256.4489	$256.45	$256.45	$256.40
Purchase #3	$136.55	13.807%	$155.4035	$155.40	$155.40	$155.40
Purchase #4	$158.67	5.110%	$166.778	$166.78	$166.80	$166.80
Purchase #5	$174.58	12.554%	$196.4968	$196.50	$196.50	$196.50
Purchase #6	$122.37	9.305%	$133.7565	$133.76	$133.75	$133.80
Purchase #7	$249.58	11.604%	$278.5413	$278.54	$278.55	$278.50
7 purchase totals =	$1,099.66		$1,198.3428	$1,198.35	$1,198.35	$1,198.30